Microglanis berbixae, Tobes & Falconí-López & Valdiviezo-Rivera & Provenzano-Rizzi, 2020

Tobes, Ibon, Falconí-López, Ana, Valdiviezo-Rivera, Jonathan & Provenzano-Rizzi, Francisco, 2020, A new species of Microglanis (Siluriformes: Pseudopimelodidae) from the Pacific slope of Ecuador, Neotropical Ichthyology (e 190023) 18 (2), pp. 1-19 : 4-14

Microglanis berbixae , new species urn:lsid:zoobank.org:act:642C180E-624E-4A11-A81F-3FEA7981E04D

( Fig. 1 , 3–7 , Tab. 1)

Holotype. MECN-DP-3944, 54.2 mm SL, male, Ecuador, Pichincha Province, Parroquia de Pacto, Quebrada Sune, a tributary of Pachijal River , Esmeraldas River Basin , Pacific slope, 0°05’28.56”N 78°53’53.04”W, 960 masl, 3 Jul 2017, I. Tobes, A. Falconí-López, J. Valdiviezo-Rivera, and F. Provenzano-Rizzi.

Paratypes. MECN-DP-3765, 4, 34.9–53.5 mm SL, same data as holotype . FMNH 135030 , 2 , 36.5-52.1 mm SL, same subsequent data as holotype . MZUSP 123411 , 2 , 34.9 –40.0 mm SL, same subsequent data as holotype . MEPN 19262 , 2 , 42.2–47.8 mm SL, same subsequent data as holotype. MECN-DP-3762, 4 (2 C, S), 39.5–51.4 mm SL, same subsequent data as holotype except for the collection date of 19 Aug 2016 .

Non-types. MECN-DP-3763, 2, 41.3–43.3 mm SL, same subsequent data as holotype except for the collection date of 19 Aug 2016. MECN-DP-3764, 1, 48.4 mm SL, Ecuador, Pichincha Province, Parroquia de Pacto, Mashpi Community, a tributary of Mashpi River , Pachijal River Basin , Esmeraldas River Basin , Pacific slope, 0°10’52.20”N 78°54’42.24”W, 539 masl, 14 Aug 2015, I. Tobes, R. Miranda, B. Ríos- Touma and A. Morabowen .

Diagnosis. Microglanis berbixae is distinguished from congeners by its color pattern. Head and body uniform, pale brown, yellowish or grayish, without any kind of blotches, bands, or dots, except a transverse lunate band, dark brown or black, at caudal-fin origin vs. head and body mottled or marbled brown with whitish or cream blotches, bands, or dots in other species ( Figs. 1–3 ). Microglanis berbixae is further distinguished from M. variegatus , its geographically closest species, by belly pigmentation; in M. berbixae the belly color is uniform, yellowish or grayish brown, without aggregates of small black dots (melanophores), while M. variegatus usually possesses a whitish or creamy belly with randomly arranged aggregates of melanophores ( Figs. 2–3 ).

In M. berbixae , fin-rays have very thin stripes, parallel, black or dark, while in M. variegatus , fin-rays have random patterns of dark spots. In M. berbixae , the adipose-fin origin and anterior area are normal, while in M. variegatus , these areas are notably lighter or luminous ( Figs. 1–3 ). Specimens of M. berbixae may have two or three black spots on adipose-fin, not observed in specimens of M. variegatus . Additionally, M. berbixae have higher values of distance between dorsal and pelvic fins than M. variegatus (24.4%–28.8% SL and 22.0%–24.1% SL, respectively) and between posterior nostrils (40.5%–52.3% HL and 24.4%–30.6% HL, respectively).

Description. Morphometric data are summarized in Tab. 1. Small-sized species, maximum size recorded 54.2 mm SL. Body depressed from snout tip to dorsal-fin origin, progressively compressed to caudal-fin base. Highest body depth at dorsal-fin origin and largest body width at pectoral-fin origin. Lateral line short, reach pelvic-fin origin, with 8 or 9(*) pores. Contour of ventral surface of head and body almost flat or slightly convex until anal-fin origin, and then slightly concave posteriorly ( Fig. 1 ). Anus and urogenital papilla are differentiable. Papilla located behind the anus as a thickened fleshy tube, with variable shape between sexes (see “Sexual dimorphism” section).

Head depressed, anteriorly rounded in dorsal view. Eyes small, more dorsal than lateral, closer to mouth than to distal margin of operculum, located near the first third of head length, covered by skin, and without free orbital margin. Snout short. Anterior nostril tubular, closer to upper lip than to eye; posterior nostril near anterior margin of eye, possess an anterior flap ( Fig. 1 ).

Mouth wide, terminal. Teeth villiform, curved backward. Gill membrane free from isthmus, with nine branchiostegal rays. All barbels thin, flattened in cross-section. One maxillary pair, two mental pairs. Maxillary barbel medium-sized, reaching or slightly surpassing pectoral-fin base. Outer mental barbel not reaching pectoral-fin base; inner mental barbel shorter, reaching almost half-length of outer mental barbel ( Fig. 1 ). Dorsal-fin I,6 rays (13*), located anterior to half of body length, posterior margin rounded, spinelet present. Dorsal-fin spine straight, strong and without hooks, shorter than first four branched rays. Adipose-fin fleshy and elongated, with free posterior margin, its origin opposite to anal-fin origin and its base a little longer than anal-fin base. Pectoral-fin I,6 rays (12*), I,5 (1), slightly triangular, when adpressed, not reaching pelvic-fin origin. Pectoral-fin spine strong, slightly flattened and curved, shorter than first two branched rays, with serrations on both margins, anterior serrations partially or weakly developed compared with posterior ones. Pelvic-fin rounded, i,5 rays (13*). Pelvic-fin origin at vertical line posterior to base of last branched dorsal-fin ray, when adpressed not reaching anal-fin origin. Anal-fin short with rounded margin, its base shorter than adipose-fin base and not confluent posteriorly with caudal-fin, ii,10 (13*). Caudal-fin truncate, 9,10 (1) or 10,10 (12*) principal rays and 7/4 procurrent rays (13*).

Osteological characters. In dorsal and ventral views of mesethmoid, the anterior edge bifurcates and forms conspicuous cornuas ( Fig 4 ). In dorsal view, central area of posterior edge constitutes the anterior margin of anterior cranial fontanelle; laterally, the posterior edge articulates with frontals ( Fig. 4A ). In ventral view, behind cornuas, bone widens and shows lateral projections smaller than cornuas, with a slightly concave anterior border ( Fig. 4B ). These projections are visible in both views ( Fig. 4 ). Ventrally, the articulation between mesethmoid and vomer is not visible, both bones are firmly united or fused, cannot be separated. Thus, the presence of a mesethmoidvomer complex is possible ( Fig. 4B ). In ventral view, the posterior edge shows elongated and pointed middle projection, which is part of the articulation between vomer and parasphenoid ( Fig. 4B ). Anterior cranial fontanelle is large, oval or elliptical, and nearly 33% of its length is located on the mesethmoid ( Fig. 4A ).

Premaxillary tooth plate trapezoidal-shaped, its distal border wide, truncate and without posterior projection ( Fig. 4C ). Dentary tooth plate elongated, larger, and narrower than premaxillary plate.

Frontal bone between mesethmoid and parieto-supraoccipital, defines lateral and posterior margin of anterior cranial fontanelle. Frontals narrow anteriorly and widened from center to back.

Parieto-supraoccipital is pentagon-shaped, in dorsal view, articulates anteriorly with frontals, and continues posterior as a process elongated and pointed, not bifurcate. Parieto-supraoccipital articulates anteriorly with sphenotic, in the center with pterotic and posterior with epiotic.

In ventral view, Weberian apparatus (complex centra) shows the transverse processes of 4th centra, expanded as anterior and posterior projections, with a concave margin at the center, anterior and posterior projections not branched, pointed. Frontal region of anterior projection flat or somewhat deflected ventrally. Transverse processes of 5th centra elongated, curved and pointed ( Fig. 5 ). Thirty vertebrae (six precaudal + 24 caudal). Six pairs of pleural ribs.

Branchial apparatus with two basibranchial and two hypobranchial elements ossified, visible. Gill rakers small and conical, first branchial arch with 2, 1, 4–5. Branchiostegal rays, 9.

On pectoral girdle, cleitrum with two projections on distal region, one dorsal, pointed, articulates with posttemporosupracleitrum and a posterior projection (cleithral spine), slender and pointed ( Fig. 6A ). On dorsal view of escapulo-coracoid bone, filamentous mesocoracoid arch is present ( Fig. 6A ). Tip of pectoral-fin spine not ossified. Anterior and posterior surfaces of pectoral-fin spine, dentate. Anterior surface with 10-12 small or weakly developed prickles, on the central and proximal sectors, distal sector without prickles Posterior surface of pectoral-fin spine with 10 prickles well-developed ( Fig. 6B ).

Coloration in alcohol. Color pattern on specimens preserved in 70% ethanol: head and body color, uniform, pale brown, yellowish or grayish, without bands, dots, blotches, or patches, except transverse lunate band, dark brown, or black at the caudal-fin base ( Fig. 1 ). Belly color uniform, pale brown, whitish or grayish, without groups of melanophores. Fins without dots, blotches, or bands; rays with very narrow dark brown or black bands or stripes, proximally and medially. Interradial membrane is hyaline, except on dorsal-fin. Dorsal-fin has dark brown interradial membrane, anterior and proximally, becoming paler or hyaline posterior and distally. Adipose-fin similarly colored as head and body, but the border is hyaline, its origin and forward without lighter or luminous areas. Three specimens with two or three dark brown or black dots, usually horizontally aligned.

Sexual dimorphism. Specimens analyzed have urogenital papilla easily detected behind anus. The papilla is a short tube, thick and fleshy, with cylindrical or triangular shape. Cylindrical-shaped papilla ending truncate with a small pointed flap is associated with females ( Fig. 7A ). Two of them were dissected, showing well-developed ovaries, with yellow ovules visible by the naked eye. Ovaries occupy important volume on posterior region of abdominal cavity. Elongate and triangular papilla, ending in point tip associated with male specimens ( Fig. 7B ). One dissected male specimen showed developed testicles as ramified bands, white, attached to the dorsal region of abdominal cavity.

Geographical distribution. Specimens were captured in two small rivers of the Pachijal River system, the Sune and Mashpi Rivers ( Fig. 8 ). These rivers belong to the Esmeraldas River Basin, Pacific Ocean versant, northwestern Ecuador, Pichincha province.

Ecological notes. Specimens were captured from two different localities. Microhabitat preferences: capture zone around the central area of the stream, characterized by shallow rapids (<20 cm; <0.3 m s-1) with pebbles and small scattered boulders. Sampling area at the Sune River located at 960 masl with a water temperature of 20.3ºC, a conductivity of 46.5 μS cm-1, dissolved oxygen with a saturation of 74.9%, and a pH of 7.8. River stretch with a mean width of 4.2 m and a mean depth of 33.1 cm. Rapids with slow velocities (<0.3 m s-1). Substrate composed as follows: sand (<2 mm) 19%; gravel (2–64 mm) 23.3%; pebbles (64–256 mm) 21.7%; boulders (> 256 mm) 22.7%; and bedrock 13.3%. Riparian forest almost intact, shading 90% of the stream ( Fig. 9 ). In one sample from the Sune River, the fish community dominated by Rhoadsia altipinna (26 specimens) and Andinoacara blombergi (12). The fish assemblage also included Astroblepus cyclopus (1), Astroblepus sp. (3), Trichomycterus sp. (2), Pseudopoecilia festae (2), and Microglanis berbixae (12).

At the Mashpi River, specimens were captured from the mouth of a small stream draining to the main channel, at 562 masl. Pphysicochemical variables were: water temperature of 23.2ºC, a conductivity of 78.7 μS cm-1, dissolved oxygen with a saturation of 89.4%, and a pH of 7.8. River stretch with a mean width of 1.9 m and a mean depth of 13.1 cm, mainly dominated by shallow rapids with slow velocities (<0.3 m s-1). Substrate composed by: sand (<2 mm) 55%; gravel (2–64 mm) 13%; pebbles (64–256 mm) 7%; and boulders (> 256 mm) 25%. The stretch totally shaded by a wellpreserved riparian forest. In one sample, the fish community composed by: Rhoadsia altipinna (15 specimens), Andinoacara blombergi (1), Bryconamericus dahli (3), Astroblepus sp. (2), Trichomycterus sp. (1), Pimelodella modesta (2) and Microglanis berbixae (1).

Etymology. The specific name “berbixae ”, honor María Resurección Sesma Lizari, “Berbixe”, mother of Ibon Tobes Sesma, for its unconditional support and infinite love. A genitive.

Conservation status. Microglanis berbixae inhabits the Tropical Andes at the Pacific slope of Ecuador. This area belongs to the Tumbes-Chocó-Magdalena hotspot ( Myers et al., 2000). The Pachijal River system drains to the Esmeraldas River basin, coastal slope of northwestern Ecuador. In the area, river systems are poorly known and Microglanis berbixae has been reported for only two localities. Consequently, the conservation status of Microglanis berbixae may be classified as Data Deficient (DD), according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN, 2019).

Morphometric comparison. After comparing the 28 morphometric characteristics between M. berbixae and M. variegatus , only two variables show intervals without overlap: the distance between dorsal and pelvic fins and the distance between posterior nostrils (see Tabs. 1–2).

Figures

FIGURE 1 | Microglanis berbixae new species, MECN-DP-3944, holotype, male 54.2 mm SL.

FIGURE 2 | Microglanis variegatus, MECN-DP 4259, male, 37.9 mm SL.

FIGURE 3 | Color pattern in live specimens. A. Microglanis berbixae, MECN-DP-3764, 48.4 mm SL. B. Microglanis variegatus, MZUTI-P-000626, 35.66 mm SL.

FIGURE 4 | Microglanis berbixae, MECN-DP 3762, paratype, 39.6 mm SL. Mesethmoid-Vomer complex. A. Dorsal view. B. Ventral view. C. Premaxillary tooth plate, ventral view. Scale bars = 1 mm.

FIGURE 5 | Microglanis berbixae, MECN-DP 3762, paratype, 39.6 mm SL.Ventral view Weberian apparatus. Scale bar = 1 mm.

FIGURE 6 | Microglanis berbixae, MECN-DP 3762, paratype, 39.6 mm SL. A. Dorsal view right pectoral girdle. The arrow shows the filamentous mesocoracoid arch. B. Dorsal view right pectoral-fin spine. Scale bars = 1 mm.

FIGURE 7 | Microglanis berbixae, close up urogenital papillae. A. Female, MECN-DP-3765, 53.5 mm SL. B. Male, MECN-DP-3765, 52.6 mm SL.

FIGURE 8 | Map of Ecuador showing capture localities of Microglanis berbixae (red dots) and Microglanis variegatus (black triangles).

FIGURE 9 | Quebrada Sune, tributary of Pachijal River, Pichincha. Type locality of Microglanis berbixae.